1. Field of the Invention
This invention relates generally to an anticipatory control technique, for an automatic control system. More specifically, the present invention relates to an anticipatory control technique for an automatic control system constituted in such a fashion that the output of a master controller operates so as to keep constant the sum of the values of operation parameters of a plurality of operation ends (appliances) equipped individually with sub-loop controllers as individual control devices, and controls the sub-loop controllers by its output.
2. Background of the Invention
An automatic control system equipped with one master controller and a plurality of sub-loop controllers, operating so as to keep constant the sum of the values of the operation parameters is applied, for example, to the following plants.
I. Combustion control of coal fired boilers in thermal power plants:
A coal fired boiler is equipped with a plurality of sets of fuel feeders, each set consisting of a pulverizer for pulverizing the coal to coal dust and a coal feeder capable of adjusting the coal feed quantity to the pulverizer, and the automatic control system described above controls the coal feed quantity to each coal feeder so that the sum of fuels charged into the boiler (or the pulverizer) is constant.
II. Power generation quantity control of gas turbine power plant:
Since the output of a single gas turbine generator is from 70,000 to 80,000 kw, a plurality of gas turbine generators are combined as one set to constitute the power plant. The fuel feed to each gas turbine is controlled on the basis of an instruction signal for the total power generated by the power plant. Power generation is mostly controlled so as to be constant also for a so-called STAG (Steam Turbine And Gas Turbine) system which further includes an auxiliary boiler using the exhaust gas of the gas turbines as the fuel, and drives a steam turbine generator with the resulting steam.
III. Feed water control to boiler of thermal power plant:
A plurality of feed water pumps are used for the boiler, each being driven by a motor or a steam turbine. In this case, the total feed water quantity must be constrolled to a predetermined quantity to correspond with the total fuel quantity or total air quantity to the boiler, and the rotating speed of a pump driving steam turbine, for example, is controlled. The pump driving motor is subjected to speed control if it is a variable speed type and to on-off control if it is not.
The automatic control system for the plants described above includes a proportioning integration component in its master controller, and is mostly equipped further with this proportioning integration function in its sub-loop controllers, too. This results in the problem that response is slow when a load demand signal for the master controller changes. In the plants described above, not all the sets are always subjected to operation control, but a suitable number of sets are controlled in accordance with the magnitude of the load demand signal. When any operation ends are started or stopped so as to control the number of sets, this control is conducted by a manually operated signal provided separately by the output of the master controller. Alternatively, the output of the master controller is added to a bias signal from a computer that is disposed separately, and the sum output is applied to a specific sub-loop controller to control its point of operation and to start or stop the operation at a particular point.
The plant and the automatic control system described above are known from 1975, ISA (Instrument Society of America), IPI 75456 (17-26) "DESIGN OVERVIEW FOR PULVERIZER CONTROL SYSTEM". This reference illustrates a fuel control system for a coal fired boiler in FIG. 1 and its controller, in FIG. 2. This system operates the plant in the manner described above and is not free from the problem described above.
To eliminate problem (or the response delay of the plant), a method which suitably adjusts the proportional gain of a controller and the time constant of an integrator may be employed, but the method is not sufficiently satisfactory. The use of anticipatory control in combination with feedback control is a known ordinary control method, but anticipatory control is not easy to practise because various operations such as number change control, manual operation, bias control, and the like, must be made. As is well known in the art, a signal for anticipatory control can not assume an arbitrary value. To fully utilize the effect of anticipatory control, an ideal value for an anticipatory control signal would be one that minimizes the necessity of correction by feedback control.